COATING SOLUTIONS

During operation gas turbine components are subject to degradation processes that affect the integrity of the parts and hence reduce the lifetime. In order to protect the parts from being damaged by (thermal) degradation processes and ensure the lifetime of the components, coatings can be applied to the components.

The type of coating is determined by the local operating conditions in the gas turbine. The Ansaldo Thomassen buckets and nozzles are supplied with coating schemes for standard operation. Under certain conditions however, a more advanced coating solution might be recommended. In such a case, Ansaldo Thomassen can provide you with advice on tailor made coating solutions that match the specific operating conditions of the parts.
The coating solution might range from thermal barrier coatings, LPPS MCrAlY coatings to a (silicon modified) aluminide or chromide diffusion coating.

The table below summarizes per 6B bucket and nozzle the standard coating configuration, as well as other typical coating solutions.

6B FIRST STAGE NOZZLE
Since the base alloy of the 6B first stage nozzle has a good oxidation and corrosion resistance, a coating is not required.

For high temperature applications however, a thermal barrier coating (TBC) on the gas path can be applied to reduce the operating metal temperature and thus increase the lifetime of the component. The thermal barrier coating is applied with the air plasma spraying coating process (APS).
To establish a reliable bonding between the ceramic TBC and the metallic base alloy, a MCrAlY bond coating is applied. The composition of the bond coating is chosen to have an increased oxidation resistance.

6B FIRST STAGE BUCKET
The 6B first stage buckets have an extended coating configuration to withstand the severe operating conditions. Externally the gas path is coated with a LPPS MCrAlY coating that is applied to improve both the hot corrosion and the oxidation resistance.

In order to increase the oxidation resistance even more, the MCrAlY coating is overcoated with a thin aluminide diffusion coating by means of a chemical vapor deposition process.

In order to improve the oxidation resistance of the material in the cooling holes as well, the cooling holes and internal cavity are coated with an aluminide diffusion coating. Finally, after shot peening, a seal coat is applied to the root serrations in order to minimize leakage of cooling air.

For high temperature applications, the operating metal temperature of the airfoil can be reduced by means of a thermal barrier coating (TBC) on the gas path.

6B SECOND STAGE NOZZLE
The 6B second stage nozzles are normally coated with an aluminide diffusion coating. The aluminium compound in the coating increases the oxidation resistance. The aluminide coating is applied by means of a chemical vapor deposition process.

6B SECOND STAGE BUCKET
Typically, the gas path of the 6B second stage buckets is uncoated. After shot peening, a seal coat is applied to the root serrations in order to minimize leakage of cooling air.
In some applications, it might be beneficial to apply an oxidation or corrosion resistant coating to the gas path. The type of coating is determined by the operating conditions and can be either a LPPS MCrAlY or a (silicon modified) aluminide diffusion coating.

6B THIRD STAGE NOZZLE
The 6B third stage nozzles are not coated.
A possible coating solution can consist of silicon modified aluminide or chromide diffusion coating on the gas path, to protect the part against hot corrosion.

6B 3RD STAGE BUCKET
Typically, the 6B third stage buckets are not coated, but under corrosive conditions a chromide coating might be applied.

EFFECTIVE TAILOR MADE COATING SOLUTIONS
Together with Ansaldo Thomassen, you can come to an effective tailor made coating solution. After assessment of the local operating conditions or circumstances that influence the performance of base alloy or coating, the best coating solution is advised.

We kindly invite you to inform us about your specific turbine operating conditions by returning the completed coating inquiry form.